[u]Note[/u]: This works for FreeBSD 5.4
Linux-firefox works better with the flash plugin (which is only available for Linux and Solaris as a binary) than the native firefox and so it is a more desirable browser to use.  Don't worry about performance, the linux-firefox runs as fast as the native build.  Be sure you are running linux_base-8 or you will have problems, generally if you said "yes" to linux binary compatibility in the installation, linux_base-8 is installed by default on FreeBSD 5.4; for 5.3 it will have installed 7.3.

If you didn't know this and annoyed by slow and jerky flash in native, go ahead and install linux-firefox
# cd /usr/ports/www/linux-firefox
# make && make install clean

If you haven't already done so
Build jdk14, linux-flashplugin7, linuxpluginwrapper, mplayer

# portinstall <app>

or

#pkg_add -r <app>

or you can cd to these corresponding directories and run
# make && make install clean

[u]Directories[/u]:
/usr/ports/java/jdk14
/usr/ports/www/linux-flashplugin7
/usr/ports/www/linuxpluginwrapper
/usr/ports/multimedia/mplayer

Note: You have to get some files manually from sun.com for jdk14, move them to /usr/ports/distfiles
Just follow the instructions that are spat out
Compiling jdk will take a while

If you want the plugins to work for the native firefox (after you installed linuxpluginwrapper)
be sure to copy libmap.conf-FreeBSD5-stable to /etc/libmap.conf

# cp /usr/local/share/examples/linuxpluginwrapper/libmap.conf-FreeBSD5-stable /etc/libmap.conf

Or if you already have a libmap.conf, copy and paste the appropriate sections of the example conf.

Now, grab the fedora core 1 mplayerplugin rpm
[url]http://prdownloads.sourceforge.net/mplayerplug-in/mplayerplug-in-2.80-1.FC1.i386.rpm?download[/url]

now extract the rpm:
# rpm --nodeps --ignoreos --install mplayerplug-in-2.80-1.FC1.i386.rpm

This will extract the file to /usr/lib/mozilla/plugins

Move the plugin to the linux-firefox plugin directory
mv /usr/lib/mozilla/plugins/mplayerplug-in.so /usr/X11R6/lib/linux-firefox/plugins/

To get flash working, create a symbolic link from the flashplugin files in /usr/X11R6/lib/browser_plugins to the linux-firefox plugins directory

# ln -s /usr/X11R6/lib/browser_plugins/*flash* /usr/X11R6/lib/linux-firefox/plugins/

Although, I find that this flash binary doesn't work as well as the one on the macromedia site and so if you experience the same problems, grab it from macromedia
[url]http://fpdownload.macromedia.com/get/shockwave/flash/english/linux/7.0r25/install_flash_player_7_linux.tar.gz[/url]

untar and run the installer script
# tar -xzf install_flash_player_7_linux.tar.gz
# cd install_flash_player_7_linux
# ./flashplayer-installer

Note: When it asks for the firefox installation, specify /usr/X11R6/lib/linux-firefox

For java, create a symbolic link from the linux-sun-jdk1.4.2 directory to the linux-firefox plugin directory
# ln -s /usr/local/linux-sun-jdk1.4.2/jre/plugin/i386/ns610-gcc32/libjavaplugin_oji.so /usr/X11R6/lib/linux-firefox/plugins

And for Acrobat and Realplayer
symlink nphelix.so and nppdf.so
ln -s /usr/X11R6/lib/browser_plugins/n* /usr/X11R6/lib/linux-firefox/plugins/

And tadda!  You have a fully operational browser

Edit:  Because FreeBSD is on the verge of a new release, there is a ports freeze in effect to ensure everything works properly on the new release.  For this reason, linux-firefox port is old and is still version 1.0.5 so feel free to try cvsup (in case a security release was made) or grab 1.0.6 it at
[url]http://download.mozilla.org/?product=firefox-1.0.6&os=linux&lang=en-US[/url]
untar it
# tar -xzf firefox-1.0.6.installer.tar.gz
# cd firefox-installer
# ./firefox-installer

Remember, to keep consistency, the path is /usr/X11R6/lib/linux-firefox

I did the same to get flash working in FF on my FreeBSD 5.4 box. 

One thing I will warn people of, do NOT install the "flashplugin-firefox" port, if it is in your ports directory still, you need to cvsup.  It was a huge flop and was removed from ports as a result. 

"/usr/ports/www/flashplugin-firefox/" is the port I am refering to.  I installed it, it didn't work for crap, so I thought there might be a new version, so I did a cvsup on my ports, only to notice... that port was selected for removal.  I deinstalled it, went the linux route (as nslay describes above) works like a charm :)

Or you could be absolutely thrilled that Flash doesn't work (or well, at least) with the native build.  Anything that keeps shitty unwanted animations and sound effects off my computer is good by me.  Hoorah!